Sewage sludge resulting from sewage treatment is often burned into ashes for disposal or into melt slags for reuse.
There has been proposed a recycling system of melt slags, in which the melt slags are pulverized so as to be reused as aggregates of a concrete product. According to this known method, melt slags are pulverized into large and small lumps to be mixed with regular aggregates for use as concrete aggregates.
Meanwhile, an interlocking block is well known as a pavement stone having a curved contact surface. The well-known interlocking block is regulated to have 50 kgf/cm.sup.2 in flexural strength and 330 kgf/cm.sup.2 in compressive strength at the time of shipment. The conventional aggregates obtained by pulverizing melt slags as set forth above cannot bear enough flexural strength and compressive strength when they are used in the interlocking blocks, so that they are usually mixed with regular aggregates.
As described above, since the aggregates obtained by pulverizing melt slags reduce the flexural and compressive strength of a concrete product which requires a given flexural and compressive strength, they cannot constitute the whole aggregates. Consequently, as a matter of fact the aggregates obtained by pulverizing melt slags are mixed with regular aggregates (gathered in classification by cracking stones or from earth and sand in riverbeds or sea coasts) up to about a third of the whole aggregates according to the conventional recycling system. Accordingly, the conventional system which uses aggregates obtained by pulverizing melt slags is not capable of recycling a large amount of melt slags since it can make use of only a little amount of melt slags. Moreover, even if the recycled aggregates are mixed with regular ones, the resulting concrete products are inevitably reduced in strength.
Furthermore, there arises another problem that the aggregates obtained by pulverizing melt slags as set forth above produces a secondary waste matter of fine powders which are produced in the pulverization process, since the fine powders is not used in the conventional method.
Accordingly, it is an object of the present invention to solve the drawbacks of the prior art set forth above and provide a concrete product which uses aggregates obtained by pulverizing melt slags or pellets and which is hardly reduced in the flexural and compressive strength thereof and does not produce the secondary waste matter since it uses 100% of the melt slags, and to provide a method of fabricating the same.